Modern grand piano actions utilize a jack or hopper to transmit key motion to the hammer, this device being disengaged as the hammer reaches the string in order that the hammer can rebound therefrom and not block the string. This action is called let off or escapement. The hammer now having escaped must, under heavy playing, be prevented from rebounding so far as to rebound in turn from the hammer rest and return again to block the string. This is done by the check, a pad which catches the hammer as it leaves the string. Finally, a last device is used, the repetition lever. This part supports a portion of the weight of the hammer so as to allow the hopper to regain a position under the hammer without complete release of the key. This provides for a rapid repeat of the hammer blow.
As is shown hereinafter, it is the object of my invention to provide a piano action which performs all four of these functions using a single mechanism, the pneumatic piston. The latter device (1) presents a reaction force to motion thereof which can be used to drive the hammer, (2) presents no resistance at zero drive velocity and so can be used to perform the escape function, (3) is intrinsically self-damping, eliminating the need for a check, and (4) presents the same reaction force regardless of position, thus enabling the repeat function.